1. Field of the Invention
This invention relates generally to a synchronizer for a vehicle transmission and, more particularly, to a synchronizer for a vehicle transmission, where the synchronizer is electrically actuated.
2. Discussion of the Related Art
As is well understood in the art, vehicles that are powered by an internal combustion engine require a transmission for shifting between gears to effectively transmit the power generated by the engine to the vehicle wheels. Modern transmissions for both manually shifted and automatically shifted gears require precise alignment between the speed of the desired shift gear and the output shaft of the transmission during a shift to prevent gear clashing, and thus gear damage. The desired shift gear is disposed around and is freely rotatable relative to the output shaft when it is not being used to deliver engine power to the output shaft of the transmission. It is necessary to synchronize the rotation of the shift gear with the output shaft of the transmission prior to the gear being engaged to the output shaft to deliver power thereto. In other words, the speed of a mating main shaft gear must be synchronized in speed to the output shaft of the transmission before the gear is engaged to the output shaft.
Synchro-mesh mechanisms or synchronizers are employed in transmissions for this purpose, where multiple synchronizers are required for multiple shift gears. A typical synchronizer includes a n inner hub that is spline mounted to the output shaft and thus rotates therewith. The hub is held in a stationary position on the output shaft between the various shift gears positioned along and freely rotatably relative to the output shaft. The synchronizer also includes an outer sleeve having internal splines that mesh with external splines on the inner hub. Thus, the outer sleeve rotates at the same speed as the output shaft.
A shift fork engages a groove in an outer surface of the outer sleeve and is actuatable to slide the outer sleeve relative to the inner hub on the meshed splines in an axial direction relative to the output shaft. The shift fork is typically driven by a mechanical actuator in a manual transmission and by a hydraulic actuator in an automatic transmission. Longitudinally extending inserts are rigidly mounted to the inner surface of the outer sleeve, and are positioned within cooperating slots on the outer surface of the inner hub.
The synchronizer also includes a blocking ring positioned between the outer sleeve and the inner hub that acts as a clutch to speed up or slow down the shift gear during a shift to match the speed of the shift gear to the speed of the output shaft. When the shift fork causes the outer sleeve to slide on the inner hub during a shift, the inserts move axially toward the blocking ring. The inner splines of the outer sleeve engage outer splines of the blocking ring. The blocking ring includes chamfered teeth along its outer edge that engage with chamfered ends of the internal splines of the outer sleeve. The inner splines of the outer sleeve also engage with straight-cut teeth on the shift gear once the speed of the gear matches the speed of the blocking ring and the sleeve. The blocking ring includes an inner cone surface that engages and fits over a cone-shaped portion of the shift gear. The blocking ring also includes slots in the end for receiving the ends of the inserts.
During a shift, a clutch disengages the input shaft of the transmission from the engine. The shift fork is actuated to cause the outer sleeve to move toward the shift gear to be engaged. As the sleeve moves, the inserts mesh with the slots in the end of the blocking ring. This causes the blocking ring to index properly with the sleeve, which is turning at the speed of the output shaft. As the outer sleeve continues to move, it pushes the blocking ring against the cone portion of the shift gear. The shift gear is unloaded because no engine power is being delivered while the clutch is disengaged. Friction between the cone surfaces of the blocking ring and the shift gear causes the shift gear to begin turning at the same speed as the outer sleeve, and thus the speed of the output shaft. As the sleeve continues to move towards the shift gear, the shift gear starts moving at the same speed as the outer sleeve which allows the splines of the sleeve to engage the straight-cut teeth of the shift gear without clashing. This locks the gear, sleeve, hub and output shaft together. The gear is now engaged with the output shaft, and the clutch is released to allow power to flow through the gear to the output shaft and the drive wheels.
As discussed above, a shift fork is positioned in a groove cut in the outer sleeve to allow the shift fork to slide the sleeve and engage the gear. The shift fork is manually actuated by a hand-operated shift lever in a manual transmission and is hydraulically actuated in an automatic transmission. Such shifting actuators are bulky and require sophisticated linkages that can be improved upon.
In accordance with the teachings of the present invention, a synchronizer assembly for a vehicle transmission is disclosed, where the synchronizer assembly is electrically actuated during a shift. The assembly includes a sleeve having an inner surface and an outer surface. A rotor is rotably mounted to the outer surface of the sleeve and a shift collar is axially mounted to the inner surface of the sleeve. The rotor is threadably coupled to the shift collar so that when the rotor rotates, the shift collar moves in an axial direction relative to the sleeve. An armature coil is electrically coupled to the rotor to cause it to rotate. Keys are rigidly secured to the shift collar to maintain the orientation of the shift collar while it moves. The shift collar locks a shift gear to the transmission output shaft during a shift.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.